Calculator Inputs
Use one overall single-column page flow. Inside the calculator, inputs are arranged in three columns on large screens, two on medium screens, and one on mobile.
Example Data Table
These sample values show how the calculator can be used across several engineering situations.
| Case | Mode | Inputs | Expected Use |
|---|---|---|---|
| DC-DC filter stage | Triangular | Ipp = 2.4 A, 100 kHz, 470 µF, 35 mΩ | Estimate RMS ripple, ESR loss, and voltage stress. |
| Buck converter output | Buck output capacitor | ΔIL = 1.8 A, 250 kHz, 330 µF, 18 mΩ | Check if output capacitor ripple rating is sufficient. |
| Boost converter input | Boost input capacitor | Iin = 5 A, D = 45%, 120 kHz, 560 µF | Approximate RMS stress and thermal loading. |
| Pulsed inverter node | Rectangular pulse | Ipk = 3.2 A, D = 30%, 80 kHz, ESR = 22 mΩ | Evaluate pulse-driven RMS current and heating. |
Formula Used
Waveform models
Triangular ripple: \( I_{rms} = \dfrac{I_{pp}}{2\sqrt{3}} \)
Sinusoidal ripple: \( I_{rms} = \dfrac{I_{peak}}{\sqrt{2}} \)
Rectangular pulse: \( I_{rms} = I_{peak}\sqrt{D} \)
Converter approximations
Buck output capacitor: \( I_{rms} \approx \dfrac{\Delta I_L}{2\sqrt{3}} \)
Boost input capacitor: \( I_{rms} \approx I_{in}\sqrt{D(1-D)} \)
Electrical and thermal outputs
Capacitive reactance: \( X_C = \dfrac{1}{2\pi f C} \)
Capacitive ripple voltage: \( V_{C,rms} = I_{rms} X_C \)
ESR ripple voltage: \( V_{ESR,rms} = I_{rms} \times ESR \)
ESR power loss: \( P = I_{rms}^2 \times ESR \)
Temperature rise: \( \Delta T = P \times \theta \)
These formulas are engineering approximations. Final design approval should always follow the capacitor datasheet, ripple frequency curves, and actual thermal measurements.
How to Use This Calculator
- Select the waveform or converter model that matches your application.
- Enter current values appropriate to that mode, such as peak-to-peak ripple, pulse peak, or average input current.
- Provide operating frequency, capacitance, and ESR so the calculator can estimate ripple voltage and heating.
- Add the datasheet ripple rating and either keep the multiplier blank or enter your own correction factor.
- Review RMS current, loading percentage, loss, hot-spot temperature, and the final assessment.
- Use the CSV and PDF buttons to save the result summary for documentation.
FAQs
1) What is capacitor ripple current?
Ripple current is the alternating current flowing through a capacitor because of switching, rectification, or pulsating loads. It creates heating inside the part, mainly through ESR.
2) Why is RMS ripple current important?
RMS ripple current links directly to heating and power loss. A capacitor can survive a high peak briefly, but excessive RMS current can shorten life or cause failure.
3) Why does ESR matter so much?
ESR converts ripple current into heat through I²R loss. Lower ESR usually reduces self-heating, lowers ripple voltage, and improves reliability under switching loads.
4) Which mode should I choose?
Choose triangular for zero-mean ramp ripple, sinusoidal for sine-like AC current, rectangular for pulses, buck output for inductor ripple at the output capacitor, and boost input for the input capacitor estimate.
5) Does higher frequency always reduce ripple stress?
Not always. Higher frequency lowers capacitive reactance, but current waveform, ESR behavior, thermal limits, and datasheet frequency correction factors still matter.
6) Why compare against datasheet ripple rating?
The datasheet ripple rating gives a tested current limit under stated conditions. Comparing calculated RMS current with that rating helps judge electrical and thermal safety margin.
7) Is the temperature result exact?
No. It is a first-pass estimate based on ESR loss and thermal resistance. Real temperature depends on airflow, mounting, nearby heat sources, and ripple frequency behavior.
8) What design margin is reasonable?
Many engineers aim to keep normal operating ripple below about 70% to 85% of the effective rating. Extra margin helps lifetime and thermal stability.